The relationship of calcium intake, source, size, solubility in vitro and in vivo, and gizzard limestone retention in laying hens.

A 10-d trial was conducted to investigate the relationship of Ca particle size (CPS), dietary Ca level (DCL), limestone source (LS), limestone solubility in vitro (LST) and in vivo (LSV), and limestone retention in the gizzard (LRG). A total of 120 molted Leghorn hens, 88 wk of age, were randomly assigned into a 2 x 3 x 4 factorial arrangement of treatments with LS (A and B), DCL (1.95, 3.72, and 5.32%), and CPS of each limestone source (average U.S. Screen Nos. 5, 8, 14, and 27). The in vitro solubility of the four respective particle sizes were 29.8, 45.8, 49.3, and 63.1% for Source A; and 36.3, 54.8, 57.7, and 67.6% for Source B. The limestone retention in the gizzard of Source A was greater than that of Source B. The limestone retention in the gizzard was increased as in vitro solubility decreased (P < 0.001) or dietary Ca level increased (P < 0.001). The in vivo solubility of the limestone was decreased as dietary Ca level increased (P < 0.001). The in vivo solubility was negatively correlated (P < 0.05) with in vitro solubility for Source A when Ca was fed at 3.72%. The data showed that larger particle size limestone (> 0.8 mm) with lower in vitro solubility (30 to 50%) was retained in the gizzard for a longer time, which increased the in vivo solubility (94% maximum). The results support the concept that larger particle size or lower in vitro solubility may increase Ca retention for layers.